Heat exchangers are used in various capacities in automotive applications. For example, all automobiles having water cooled engines employ a radiator and a heater core. Automobiles equipped with air conditioning also include an evaporator and a condenser. These heat exchangers are made from aluminum and consist of two spaced header tanks interconnected by flow tubes having cooling fins extending therefrom. Fluid is circulated through the header tanks and flow tubes to effect the necessary temperature drop.
The header tanks, flow tubes, and cooling fins are rigidly attached to one another by brazing. It has been found that this brazing operation can be most efficiently accomplished in a furnace for mass production applications. Further, it has been found that dividing the furnace into varying zones independently controlled to raise the temperature of the workparts to a predetermined level can be utilized to produce improved braze joints. The zones are created by forming a braze furnace housing from a plurality of tubular shell sections arranged in end-to-end fashion with a partition between each shell section. One example of a multi zone furnace may be found in U.S. Pat. No. 3,756,489 to Chartet, issued Sep. 4, 1973.
The prior art is deficient in that, because the temperature between the various shell sections varies from zone to zone, the degree of thermal expansion and contraction varies from zone to zone creating stress fractures which are not adequately anticipated and prevented. Hence, the prior art is deficient in that satisfactory expansion joints are not provided between the various zones.